Do I need to tell my employees?

Yes — tell them clearly, before you start, what is recorded and why. It builds trust and is what the law expects in most countries.

A simple way: a short note or policy saying that Timerfly records work time, apps and websites during work hours (and screenshots, if on), who can see it, and how long it’s kept. Timerfly never records keystrokes, and nothing outside the work day.

This is general information, not legal advice; your lawyer can tell you what applies to you.